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I don't know about Russian and WaMu, specifically, but most banks have an idea of their customer's demographics, and target their services accordingly. That WaMu has introduced Chinese and Russian certainly tells you something about either their existing clientele or target demographic.
You didn't say, but it may also be possible that the language choices were selected based on the demographics of the machine's neighborhood. Russian here and Korean someplace else. Why not. It would make a lot of sense for WaMu to have specific language options, since they (and most major banks) are trying to increase the services provided by their ATMs, both to customers and non-customers alike, and targeting their language options accordingly might be one way to get a leg up on the competition.